C - return multiple (string) values

gistfile1.c

/*  Output multiple (string) values
    defined in a function
    to main function.

    Based on solution #2 of accepted answer in this Stack Overflow thread:
    https://stackoverflow.com/questions/2620146/
    how-do-i-return-multiple-values-from-a-function-in-c
*/

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

void getValues(char** a, char** b) {
    /*  Make sure a and b are not pointing to NULL */
    assert(a);
    assert(b);
    *a = "hello";
    *b = "world";
}

int main() {
    char* a = (char*)malloc(sizeof(char)*256);
    char* b = (char*)malloc(sizeof(char)*256);
    getValues(&a, &b);
    printf("a is %s\nb is %s\n", a, b);
}